Hybrid operating machines, for example, hybrid shovels using electricity storage cells, such as chargeable secondary cells or electric double layer capacitors, are being developed. Plate-like electricity storage cells in which an electricity storage element is wrapped with a film are proposed as electricity storage cells adopted for the hybrid operating machines. A positive electrode and a negative electrode are led out from an outer peripheral portion of an electricity storage cell.
An electricity storage module is formed by stacking and connecting a plurality of electricity storage cells in series. The electrodes of electricity storage cells adjacent to each other in the stack direction are electrically connected by welding, caulking, or the like. An electricity storage cell of the structure in which positive electrode plates and negative electrode plates are stacked via a separator and are sealed with a laminate film is proposed.